"The answer is yes," Elias Zerhouni told a Senate panel this week when asked if he believes the limit is stifling efforts to find new medical breakthroughs. "It is very clear from my point of view that the current cell lines will not be sufficient to do the research we want to do . It's not possible for me to see how we can continue the momentum of science and in stem cell research with the lines we currently have."

"It is clear today that American science will be better served and the nation would be better served if we let our scientists have access to more cell lines," added Zerhouni, who was appointed by Bush to head the NIH in 2002.

Vowing to "always stick to the scientific truth" and that "disease knows no politics," the NIH chief dismissed arguments that adult stem cells negate the need for embryonic stem cell research.

"They do not hold scientific water" he testified. "It is in the best interest of our scientists, our science, our country that we find ways—that the nation finds a way—to allow the science to go full speed on both adult and embryonic stem cell research."

The surprising but powerful testimony comes just weeks before the Senate is set to vote on legislation—passed by the House in January—that would free up federal funds to conduct research on cells taken from human embryos, which are considered by scientists to be the most promising source of potential new treatments for spinal cord injuries and degenerative diseases like Alzheimer's, Parkinson's and cancer.

Opponents argue that it is immoral and unethical to spend taxpayer dollars for research that involves destroying embryos. But advocates note that the bill—which sets up ethical and reporting guidelines—calls for expanding research only on stem cells extracted from embryos slated to be discarded by in vitro fertility clinics and only with the consent of the donors of those embryos.

Bush last year, in his only veto to date, nixed similar legislation, limiting federally funded research to 21 approved lines of embryonic cells that were created on or before August 9, 2001, even though scientists, including Zerhouni, say they have been compromised or corrupted.

The Senate is expected to easily pass the legislation, but Bush has vowed another veto despite surveys showing that the American public overwhelmingly supports embryonic stem cell research.

Tom Reynolds, a spokesperson for Sen. Tom Harkin (D-Iowa), a sponsor of the Senate measure, says the senator believes he can muster the two thirds majority—or 67 Senate votes—needed to override a veto. "We are confident that given the role the stem cell issue played during the midterm elections [when the Democrats regained control of the House and Senate]," he says, "that we should be able to find the votes we need."

In the wake of the federal ban, several states have passed measures allocating funding for embryonic stem cell research. But Zerhouni told lawmakers that the NIH—and not the states—should take the lead in this effort.

"The role that NIH has played has been second to none. There is no state that can really provide this depth and oversight," he said. "This is not a one-mile race. This may be a marathon and it is important for NIH to play its historical role.

"If you have a patchwork of different approaches," he added, "it will be very difficult for our country to muster its strength. We cannot be second-best in this area. I think it is important for us not to fight with one hand behind our back on this. To sideline NIH is shortsighted. We need to find a way to move forward. I hope we can do that soon."

In threatening a veto in January, Bush said the legislation "would use federal taxpayer dollars to support and encourage the destruction of human life for research." A White House spokesperson said that Zerhouni was free to express his opinion but that Bush would not be swayed.

Harkin applauded Zerhouni for his "courage" and "candor on a subject so important to millions of Americans suffering from illnesses such as Parkinson's, diabetes, cancer or spinal cord injuries.¿¿¿¿

"Dr. Zerhouni made a powerful statement that science, not politics should drive the discussion on lifting the ban on federal funding for human embryonic stem cell research," Harkin said. "My hope is that the White House gets the message and doesn't continue to stand in the way of progress."